1. Field of the Invention
The present invention relates to systems and techniques for guiding, steering, and advancing invasive medical devices such as catheters and catheter-type devices.
2. Description of the Related Art
In general, catheterization is performed by inserting an invasive device into an incision or a body orifice. Secondary tools such as guidewires and balloons are often advanced along the primary catheter to the area where the medical procedure is to be performed. These procedures rely on manually advancing the distal end of the invasive device by pushing, rotating, or otherwise manipulating the proximal end that remains outside of the body. Real-time x-ray imaging is a common method for determining the position of the distal end of the invasive device during the procedure. The manipulation continues until the distal end reaches the destination area where the diagnostic or therapeutic procedure is to be performed. This technique requires great skills on the part of the operator that can only be achieved after a protracted training period and extended practice. A high degree of manual dexterity is also required.
For example, angioplasty involves advancing a balloon catheter over a previously placed guidewire into a narrowed arterial section. Once properly positioned in the narrowed arterial section, the balloon is inflated and dilates this section. The time consuming technical difficulties encountered during angioplasty procedure are similar to those associated with angiography. If the artery to be treated is torturous with sharp bends, it may be difficult to advance the guidewire to the stenosis. If the stenosis is severe or the artery is totally blocked, it may be difficult or even impossible to properly position the guidewire. Alternatively, if the guidewire is successfully positioned in tight, hard plaque, the balloon catheter, being of a necessarily larger diameter than the guidewire, may encounter sufficient resistance to cause the guiding catheter to disengage from the ostium. This eliminates the support required to facilitate balloon advancement. These technical difficulties can render the procedure unfeasible.
Because of the difficulty involved in advancing a catheter into a desired location in the body, many diagnostic and therapeutic procedures employ a guidewire. The guidewire is first advanced into the heart or the artery and serves as a track and guide for a specific catheter. This technique is used to advance a catheter into the left ventricle and is especially important when studying aortic stenosis. Crossing the narrowed valve orifice is a challenge to the operator. Similarly, a guidewire is often manipulated into a blocked coronary artery and across the obstructive plaque. A therapeutic catheter, for example carrying a balloon, a laser, a stent, etc., is advanced over the guidewire, and placed at the site of the plaque. The narrowed site is then opened by inflating a balloon, operating a laser beam, or placing a stent. On occasions, the artery is torturous and severely narrowed and the plaque is irregular, calcified, or even totally occluding the artery. In these situations the placement of a guidewire beyond the narrowed site is very difficult and many times unsuccessful.
In some procedures, a catheter is used to cut through the intra-atrial septum in order to create a shunt (in transposition of the great vessels), to treat the mitral valve (mitral valvuloplasty), or to monitor directly the pressure in the left atrium.
The implantation of cardiac pacemakers is often essential for the survival of patients with heart rhythm or electrical conduction disturbances. This procedure is performed by the implantation of a small electrode in the heart cavity wall (ventricle or atrium). The other end of the electrode is attached to an electronic device which is implanted under the chest skin and that generates stimulation pulses to simulate the heart rhythm. Similar devices apply electrical shock when life-threatening heart electrical disturbances are detected by the electrodes (e.g., an Automatic Implantable Cardiac Defibrillator (AICD)). These electrodes are placed through a vein by pushing and manipulating under x-ray. Many times, the manipulation to place the electrodes in a proper position is difficult and the results are sub-optimal due to anatomical variations.
During electrophysiological study, electrical signals occurring in the myocardium (heart muscle) are measured and recorded. This is accomplished by advancing an electrode-carrying catheter into the heart. The catheter is manipulated until the electrode touches the endocardial region of interest. This can be a cumbersome and time-consuming procedure because multiple measurements are often required to perform a complete study. In addition, accurately positioning the electrode using manual manipulation is a difficult process.
Ablation of electrical pathways to eliminate heart rhythm disturbances eliminates potentially life threatening abnormal heart rhythms by ablating erroneous electrical pathways in the myocardium, that have been previously identified during an electrophysiological study. Ablation of these pathways using thermal or microwave energy delivered to a predetermined specific region by an energy-carrying catheter is the mainstay of the procedure. This catheter is placed in good contact with the selected endiocardial region, otherwise no ablation will occur. Additionally, the catheter must be precisely positioned in order to avoid damaging the normal electrical pathways. Given these exacting requirements, the imprecise nature of manual manipulation can cause this procedure to be especially difficult and time consuming.
Mitral valvuloplasty is used to treate mitral valve stenosis by dilating the narrowed valve with a balloon. The current method involves advancing a catheter through the vena cava into the right atrium. An incision is made in the intra-atrial septum and the catheter is forced through the cut into the left atrium. A balloon is then advanced through the catheter into the mitral valve apparatus, and inflated to break the stenotic tissue. Notwithstanding a high success rate and a low risk of recurrent restenosis associated with this procedure, a known complication is an atrial septal defect induced by the puncture of the intra-atrial septum. Although much less aggressive than surgery, this procedure is lengthy, difficult, and requires special skills in addition to those normally requisite for catheterization.
Mitral valvuloplasty (aorta to left atrium method) is considered by some to be a preferred alternative to the vena cava approach because the intra-artrial septum puncture is eliminated, thereby eliminating the potential complication of atrial septal defect. This procedure differs from the current method of mitral valvuloplasty in that the catheter is advanced through the aorta, the left atrium, and the aortic valve, for positioning into the left ventricle. A balloon is then advanced through the catheter into the mitral valve apparatus and inflated to break the stenotic tissue. Because a relatively rigid balloon is required to break the tissue narrowing the mitral valve, it is almost impossible to bring the balloon into proper alignment via the aorta and left ventricle due to the sharp acute angle between the aortic route and the required approach to the mitral valve.
Myocardial revascularization is a therapeutic procedure that increases the blood supply to the heart muscle by inducing the formation of new small blood vessels in the myocardium. The surgery involves opening the chest wall and laser “drilling” multiple small channels from the heart external aspect (epicardium).
Percutaneous myocardial revascularization is a catheter-based procedure for promoting angioneogensis. It involves advancing a laser catheter into the heart and performing the channelling from the heart inner aspect (endocardium). This approach is particularly applicable to patients who constitute a high surgical risk and who are beyond conventional catheter based therapy. Due to the accuracy required when positioning and fixating the laser catheter, this procedure does not appear to be implementable with currently available catheter technology.
The foregoing procedures suffer from numerous disadvantages and limitations. A very high skill level is often required to properly manipulate the catheter into position. Extensive training is required to attain this skill level. Many of the procedures are tedious and time-consuming. This results in repeated and prolonged exposure of the patient and staff to the adverse effects of x-rays. The lengthy procedures also require the use of additional contrast material with associated risk to the patient. Procedures that require highly-accurate positioning of the catheter distal end (also referred to as the catheter tip) are difficult to perform and are not always feasible. The insertion, removal, and manipulation of secondary tools often causes the tip of the guiding catheter to be dislodged from the desired position. Time-consuming manipulation is required to correctly reposition the tip. The coronary arteries are sometimes torturous with sharp bends or blockages that make advancement of a guidewire or balloon difficult or even impossible. A principal source of catheter tip location information is the x-ray imaging system with its associated adverse side effects.
Therefore, there is a great and still unsatisfied need for an apparatus and method for guiding, steering, and advancing invasive devices and for accurately controlling their position; for providing three dimensional imaging; and for minimizing the use of x-rays or other ionizing-type radiation